1. Field of the Invention
The present invention relates to an electron source and an image forming device using the electron source.
2. Description of the Related Art
Thin and planar image forming devices have been actively developed as display devices due to their efficient use of installation spaces. For example, a liquid crystal display device has been popularly used for a display member of portable type personal computers. However, the liquid crystal display device has the problems of dark image, difficulty of making the panel size large, and narrow angle of vision. Consequently, a spontaneous light emission type display has been noticed. The spontaneous light emission display using a plasma display and an electron emission element is more luminous and has a wider angle of vision as compared with the liquid crystal display.
The electron emission element is mainly divided into two categories of a thermionic emission element and cold emission element. The cold emission element include field emission type (abbreviated as a FE type hereinafter), metal/insulation layer/metal type (abbreviated as a MIM type hereinafter) and surface conduction type electron emission elements. Examples of the FE type elements include those disclosed in P. Dyke and W. W. Dolan xe2x80x9cField Emissionxe2x80x9d, Advance in Electron Physics, 8, 89 (1956) and C. A. Spindt, xe2x80x9cPhysical Properties of Thin-film Field Emission Cathode with Molybdenum Conesxe2x80x9d, J. Appl. Phys., 47, 5248 (1976). Examples of the MIM type elements include those disclosed in A. Mead, xe2x80x9cOperation of Tunnel-Emission Devicesxe2x80x9d, J. Aply. Phys., 32, 646 (1961).
Examples of the surface conduction type electron emission elements include those disclosed in M. I. Elinson, Radio Eng. Electron Phys., 10, 1290 (1965). The surface conduction type electron emission element takes advantage of a phenomenon by which electrons are emitted by flowing an electric current in parallel to the film surface formed as a small area thin film on a substrate. These surface conduction type electron emission elements include those using a SnO2 thin film reported by Elinson et. al., using an Au thin film [G. Dittmer, xe2x80x9cThin Solid Filmsxe2x80x9d, 9, 317 (1972)], using an In2O3/SnO2 thin film [M. Hartwell and C. G. Fonstad, xe2x80x9cIEEE Trans. ED Conf.xe2x80x9d, 519, (1975)], and using a carbon thin film [Hisashi Araki, xe2x80x9cSinku (Vacuum)xe2x80x9d, vol. 26, No. 1, p22 (1983)].
FIGS. 13A and 13B show one example of the surface conduction type electron emission element. FIG. 13A is a plane view and FIG. 13B is a cross section. The reference numeral 6 denotes an insulation substrate, the reference numerals 2 and 3 denote element electrodes for attaining electrical connection, the reference numeral 4 denotes a conductive film, and the reference numeral 5 denotes an electron emission part. FIG. 8 shows a schematic drawing of one example of the image forming device using an electron source formed by aligning the surface conduction type electron emission elements in a matrix.
The construction of the element shown in FIGS. 13A and 13B is a construction of a unit element, and a number of these unit elements 76 are aligned on the substrate (a rear plate) 81 corresponding to pixels, thereby forming an electron source in the image forming device shown in FIG. 8. Wiring lines 72 in the X-direction and wiring lines 73 in the Y-direction are formed on the substrate 81 by being separated by an insulation layer (not shown) forming a matrix of the wiring lines in order to arbitrarily select each element. A glass plate is often used for the substrate 81.
The reference numeral 88 denotes an external case and the reference numeral 86 denotes face plates in the image forming device shown in FIG. 8. Bonding portions among the external case 88, rear plate 81 and face plates 86 are bonded (sealed) with a binder such as a low melting point glass frit (not shown) to constitute an airtight vessel for evacuating the inside of the image forming device. The vessel is usually sealed by fusion of the frit glass. The heating temperature is typically about 400 to 500xc2x0 C., and the heating time is typically 10 minutes to 1 hour, although it differs depending on the size of the external case 88.
A blue sheet glass is preferably used as the material of the external case 88 because it can be easily and certainly fused with the frit and because it is relatively cheap. A high distortion point glass having a high distortion point prepared by substituting a part of Na with K may be preferably used since it is also readily fused with the frit. The blue sheet glass or the high distortion point glass may be also preferably used for the substrate 81 since these materials can be certainly fused with the external case 88.
A fluorescent film 84 made of a fluorescent substance is formed on the lower face of the face plate 86. A metal back 85 made of, for example, Al is formed on the rear plate side surface of the fluorescent film 84. The fluorescent film is divided into three portions coated with three kinds of fluorescent substances (not shown) having primary colors of red (R), green (G) and blue (B), respectively. The colored fluorescence films forming the fluorescence film 84 are separated with black films (not shown).
The inside of the airtight vessel is evacuated at a pressure of as low as 10xe2x88x924 Pa or below. The distance between the rear plate 81 on which the electron emission elements are formed and the face plate 86 on which the fluorescent film 84 is formed is usually maintained at several hundreds micrometers to several hundreds millimeters.
The image forming device as hitherto described is addressed by applying a voltage to each electron emission element 76 through terminals Doxl to Doxm and Doyl to Doym at the outside of the vessel, and the wiring lines 72 and 73 to emit electrons from each element 76. A high voltage is simultaneously applied to the metal back 85 through a terminal Hv at the outside of the vessel, thereby accelerating the emitted electrons from each element 76 and allowing the electrons to collide with each corresponding fluorescent substance. The fluorescent substance is excited and emits a light by collision of the electrons.
While the substrate of the electron source (rear plate) having the wiring matrix on it described above may be formed by various methods, all the element electrodes and wiring lines can be manufactured by a photolithographic method.
Printing methods such as a screen printing and offset printing may be diverted for manufacturing the substrate for the electron source. The printing methods are suitable for forming a pattern of a large area screen, and are preferable for facilitating to align a number of the electron emission elements on the substrate. For example, Japanese Patent Laid-Open Nos. 08-185818, 08-034110, 08-236017 and 09-283061 disclose a method for manufacturing the rear plate by the printing method, and a method for forming the wiring lines in the X-direction, interlayer insulation layer and wiring lines in the Y-direction by screen printing.
One example of the method for manufacturing the electron source substrate disclosed in the patent publications cited above is described with reference to FIGS. 14A to 14E. At first, a pair of the element electrodes 2 and 3 are formed on the rear plate 81 as a matrix (FIG. 14A). Then, n lines of the wiring lines 73 in the Y-direction are printed with a paste containing conductive material particles so that the electrodes 2 are commonly connected, and the printed wiring lines are fired (FIG. 14B). Subsequently, the insulation layer 74 is printed with a paste containing insulating particles (glass particles) into a comb teeth shape followed by firing (FIG. 14C). Then, a paste containing a conductive material is printed so that the wiring lines 72 in the X-direction is commonly connected 25 to the electrodes 3 on each insulation layer 74, followed by firing (FIG. 14D). A conductive film 4 is formed thereafter so as to connect the element electrode 2 to the element electrode 3 (FIG. 14E). Finally, a gap is formed at a part of the conductive film by flowing an electric current through the conductive film 4 to form an electron emission part 5.
Low resistance metals such as Al, Cu, Ag and Pt are favorable for allowing an image to uniformly display on the entire surface of a large area display screen that is currently expected in the market. Ag is in particular a preferable wiring material for printing the wiring lines since it is readily printed as a paste. While Pt is preferably used as the element electrode material since it is suitable for printing and has high heat resistance, the material cost is high.
When the unit element of the surface conduction type electron emission elements in the electron source as shown in FIGS. 13A and 13B is addressed for a long period of time, on the other hand, Na ions in the substrate are localized on the surface of the substrate due to the electric field, sometimes causing deterioration of the electron source characteristics. Deterioration of the electron source characteristics as used herein refers to a phenomenon by which the electric current flowing between the two electrodes (referred as an xe2x80x9celement currentxe2x80x9d or xe2x80x9cIfxe2x80x9d) decreases as a function of the addressing time when a voltage is applied between a pair of the element electrodes of the surface conduction type electron emission elements. Decrease of the element current causes decrease of the electric current discharged in a vacuum (referred as xe2x80x9celectron emission currentxe2x80x9d or xe2x80x9cIexe2x80x9d), and the image is gradually darkened in the image forming device using a fluorescent substance as an image forming member.
Deterioration of the electron source characteristics may be avoided in the unit element by blocking Na by forming a film by forming a film mainly comprising SiO2 on the surface of the glass substrate containing Na.
However, metal ions, for example Ag ions when the wiring material is Ag, diffuse from the wiring material into the uppermost layer formed for blocking Na as described above, or into the layer formed for suppressing electrification of the uppermost layer of the substrate in some cases, at the temperature for bonding the glass frit when the image display device is evacuated, or by the heat when the image display device is addressed. As a result, Na ions tend to readily diffuse from the substrate into the electron emission part, or the metal ions themselves tend to readily diffuse into the electron emission part, thereby deteriorating the electron source characteristics.
Accordingly, it is an object of the present invention to provide a luminous and high quality image display device by suppressing the electron source characteristics from deteriorating by blocking metal ions from diffusing from the wiring lines at the bonding temperature of the glass frit when the image display device is evacuated, or by the heat generated during addressing the image display device.
The present invention provides an electron source comprising a substrate, an antistatic film formed on the substrate, plural electron emission elements disposed on the antistatic film, and wiring lines containing a metal for connecting the plural electron emission elements. The electron emission element comprises a conductive film including an electron emission part disposed on the antistatic film. The conductive film is connected to the wiring lines with a conductive member for blocking the metal contained in the wiring lines from being transferred to the conductive film.
The present invention also provides an electron source comprising a substrate, an antistatic film formed on the substrate, plural electron emission elements disposed on the antistatic film, and wiring lines containing a metal for connecting the plural electron emission elements. The electron emission element comprises a conductive film including an electron emission part disposed on the antistatic film. The conductive film is electrically connected to the wiring lines via a conductive member provided between the wiring lines and antistatic film for blocking the metal contained in the wiring lines from being transferred to the conductive film.
The present invention further provides an electron source comprising a substrate, an antistatic film formed on the substrate, plural electron emission elements disposed on the antistatic film, and wiring lines containing a metal for connecting the plural electron emission elements. The electron emission element comprises a pair of electrodes disposed on the antistatic film and a conductive film including an electron emission part disposed between and connected to a pair of the electrodes. The conductive film is connected to the wiring lines with a pair of the electrodes, and a pair of the electrodes is composed of a conductive member for blocking the metal contained in the wiring lines from being transferred to the conductive metal.
The present invention further provides an electron source comprising a substrate containing sodium, a sodium blocking film formed on the substrate, plural electron emission elements disposed on the sodium blocking film, and wiring lines containing a metal for connecting the plural electron emission elements. The electron emission element comprises a conductive film including an electron emission part disposed on the sodium blocking film. The conductive film is connected to the wiring lines with a conductive member for blocking the metal contained in the wiring lines from being transferred to the conductive film.
The present invention further provides an electron source comprising a substrate containing sodium, a sodium blocking film formed on the substrate, plural electron emission elements disposed on the sodium blocking film, and wiring lines containing a metal for connecting the plural electron emission elements. The electron emission element comprises a conductive film including an electron emission part disposed on the sodium blocking film. The conductive film is electrically connected to wiring lines via a conductive member provided between the wiring lines and the sodium blocking film for blocking the metal contained in the wiring lines from being transferred to the conductive film.
The present invention further provides an electron source comprising a substrate containing sodium, a sodium blocking film formed on the substrate, plural electron emission elements disposed on the sodium blocking film, and wiring lines containing a metal for connecting the plural electron emission elements. The electron emission element comprises a pair of electrodes disposed on the sodium blocking film and a conductive film including an electron emission part disposed between and connected to a pair of the electrodes. The conductive film is connected to the wiring lines with a pair of the electrodes, and a pair of the electrodes is composed of a conductive member for blocking the metal contained in the wiring lines from being transferred to the conductive film.
The present invention further provides an electron source comprising a substrate, a film of an insulation material provided on the substrate and containing a metal oxide, plural electron emission elements disposed on the film of an insulation material containing the metal oxide, and wiring lines containing a metal for connecting the plural electron emission elements. The electron emission element comprises a conductive film including an electron emission part disposed on the film of an insulation material containing the metal oxide. The conductive film is connected to the wiring lines with a conductive member for blocking the metal contained in the wiring lines from being transferred to the conductive film.
The present invention further provides an electron source comprising a substrate, a film of an insulation material provided on the substrate and containing a metal oxide, plural electron emission elements disposed on the film of an insulation material containing the metal oxide, and wiring lines containing a metal for connecting the plural electron emission elements. The electron emission element comprises a conductive film including an electron emission part disposed on the film of an insulation material containing the metal oxide. The conductive film is electrically connected to the wiring lines via a conductive member for blocking the metal contained in the wiring lines from being transferred to the conductive film provided between the film of an insulation material containing the metal oxide and the wiring lines.
The present invention further provides an electron source comprising a substrate, a film of an insulation material provided on the substrate and containing a metal oxide, plural electron emission elements disposed on the film of an insulation material containing the metal oxide, and wiring lines containing a metal for connecting the plural electron emission elements. The electron emission element comprises a conductive film including a pair of electrodes disposed on the film of an insulation material containing the metal oxide and an electron emission part disposed between and connected to a pair of the electrodes. The conductive film is connected to the wiring lines with a pair of the electrode, and a pair of the electrodes is composed of a conductive member for blocking the metal contained in the wiring lines from being transferred to the conductive film.
The present invention further provides an electron source comprising a substrate, a SiO2 film provided on the substrate and containing a metal oxide, plural electron emission elements disposed on the SiO2 film containing the metal oxide, and wiring lines for connecting the plural electron emission elements. The electron emission element comprises a conductive film containing an electron emission part disposed on the SiO2 film containing the metal oxide. The conductive film is connected to the wiring lines with a member comprising In2O3xe2x80x94SnO2 as a constituent.
The present invention further provides an electron source comprising a substrate, a SiO2 film provided on the substrate and containing a metal oxide, plural electron emission elements disposed on the SiO2 film containing the metal oxide, and wiring lines for connecting the plural electron emission elements. The electron emission element comprises a conductive film containing an electron emission part disposed on the SiO2 film containing the metal oxide. The conductive film is electrically connected to the wiring lines via a member comprising In2O3xe2x80x94SnO2 as a constituent provided between the SiO2 film containing the metal oxide and the wiring lines.
The present invention further provides an electron source comprising a substrate, a SiO2 film provided on the substrate and containing a metal oxide, plural electron emission elements disposed on the SiO2 film containing the metal oxide, and wiring lines for connecting the plural electron emission elements. The electron emission element comprises a pair of electrodes disposed on the SiO2 film containing the metal oxide and a conductive film including an electron emission part disposed between and connected to a pair of the electrodes. The conductive film is connected to the wiring lines with a pair of the electrodes, and a pair of the electrodes comprises In2O3xe2x80x94SnO2 as a constituent.
The present invention provides an image display device comprising an electron source and an image display member for displaying an image by electron irradiation from the electron sources. The electron source may be any one of the foregoing electron sources.
Further objects, featured and advantages of the present invention will become apparent from the following descriptions of the preferred embodiments with reference to the attached drawings.